1. Field of the Invention
The subject invention pertains to the field of gallium arsenide semi-conductors and, more particularly, to a method of fabricating gallium arsenide (GaAs) devices using vapor phase epitaxial deposition with selective orientation.
2. Description of the Prior Art
As semiconductor and communications technology moved into the millimeter wave region, there has developed a need for semiconductor devices that are compatible with monolithic integrated circuits. That is, integrated circuits where at least one element thereof is formed upon or within a semi-insulating substrate. High performance mixer diodes, for example, require a heavily doped layer several microns thick beneath the active layer to reduce series resistance and to provide a corresponding high cutoff frequency. Fabrication of such devices in monolithic form have heretofore been difficult to achieve. Previous methods of providing device isolation through the heavily doped region have included: mesa etching, which leaves the surface non-planar; proton bombardment in which the thickness of the heavily doped layer is limited by the accelerating voltage of the implanter; and selective epitaxial deposition which offers the advantage of high carrier mobility and low dislocation density but often results in poor surface morphology and edge overgrowth. Irregular surface morphology and non-uniform vapor phase epitaxial growth of active regions has been a continuing problem that may interfere with further processing steps and hinder device performance. See Shaw, "Selective Epitaxial Deposition of Gallium Arsenide in Holes", J. Electro-Chemical Soc. pp. 904- 907, September 1966, and Yang, et al, "Selective Epitaxial Growth of GaAs by Liquid Phase Electroepitaxy, J. Electrochemical Soc., pp 194-197, January 1982. The non-uniform growth rate of active GaAs regions, as it is grown in the prepared holes, is a result of more than one growth plane being exposed on the sidewalls and bottom of the etched holes in which the vapor phase epitaxial growth is to take place.
The present invention provides a method for inhibiting unwanted vapor phase epitaxial growth on the sidewalls of the holes in which the active regions are grown by covering the sidewalls with a dielectric prior to vapor phase epitaxial deposition of the active area.